PHILOSOPHICAL TRANSACTIONS OF 
ted heat, and ina state of vapour, in 
closed vessels. The alloy is of a grey 
colour when the proportion of arsenic is 
considerable, extremely fusible and brit- 
tle. If the arsenic is about 1-900th of the 
gold, the alloy retains the colour of gold, 
and, though brittle, bends in some de- 
gree before it breaks. 
Antimony, either in fusion or a state 
of vapour, unites eagerly with gold, and 
in the proportion of 1-1920th destroys its 
ductility. 
Zinc is also highly injurious to the 
ductility of gold, from which, however, 
it may be separated by heat; but this is 
hot easily effected if, instead of pure zinc, 
‘brass is made use of. 
Cobalt, in the proportion of four grains 
to an ounce of standard gold, begins to 
impair its ductility and colour. When 
it amounts to nineteen grains, the alloy 
becomes of a pale yellow colour, is brit- 
tle, and exhibits a fine-grained earthy 
fracture, : 
Nickel does not begin to render stan- 
dard gold brittle in a smaller proportion 
than eight grains to the ounce.. 
Manganese unites with gold and ren- 
ders it brittle, and is itself at the same 
time protected by the gold fromthe ac- 
tion of those metals which usually dis- 
solve it. : 
» Bismuth and lead have nearly the same 
effect as antimony; an alloy of standard 
gold, containing 1-19C0th of either of 
these metals, being entirely destitute of 
ductility. If they are added in the propor- 
tion of half a grain in the troy ounce of 
standard gold, the alloy becomes re- 
markably spongy, and sutfers a diminu- 
tion of specific gravity. 
Yin, in the proportion of eight grains 
in the ounce of standard gold, renders 
the alloy somewhat pale, but does not in 
the least degree aifect its ductility; the 
bar may also be annealed at a low tem- 
perature without injury; but at a heat 
approaching the cherry red, or ten degrees 
of the pyrometer, the surface of the bar 
began to be covered with minute blisters 
or bubbles; it then curled up or warped 
on the edges, and after a time a com- 
plete solution of continuity followed, the 
bar falling down by its own weight from 
the supporters, in the form of a rough 
dark-coloured mass, having scarcely any 
metallic appearance. Hence it appears, 
that the assertions of I,ewis and other 
chemists, respecting the remarkably ill 
effect produced on gold by a scarcely 
ascertainable quantity of tm, are erro- 
THE ROYAL SOCIETY OF LONDON, 891 
neous, and probably originate from the 
lead, antimony, or bismuth, with which 
the tin may have been contaminated. 
Iron, whether in the state of bar, or 
cast iron, or cast steel, unites with gold 
in the proportion of 1-]2th, forming am’ 
alloy of a dull white colour, considerably 
harder than standard gold, but perfectly 
ductile, 
Emery does not combine with gold. 
Platina with gold forms a yellowish 
white ductile alloy. 
Copper, when pure, in the proportion 
of 1-12th, if alloyed with gold, produces 
a deep reddish yellow perfectly ductile al. 
loy.. But many of the varieties of cop- 
per in commerce that are reckoned pure 
are not sufficiently so for mixing with 
gold, probably of account of a minute 
proportion of lead or antimony, as these 
may exist in the proportion of 1-120th 
without materially afiecting the colour, 
ductility, or specific gravity of copper ; 
yet when this copper is employed in the 
usual quantity for alloying gold, the 
mass will contain 1-1440th orlead, which 
we have already seen tobe more than 
enough for rendering gold perfectly 
brittle. 
The conclusion which Mr. Hatchett 
draws from the experiments of this sec- 
tion is, that only two metals, viz. copper 
and silver, are proper for,the alloy of 
gold coin, as all the others either alter its 
colour or injure its ductility. 
The second section treats of the spe- 
cific gravity of gold when alloyed by va- 
rious metals. In this Mr. Hatchett de- 
tails the results of several experiments 
to show, that the specific gravity of gold 
alloyed with other metals is by no means 
that which results from a calculation of 
the respective densities of the component 
ingredients. ‘The effects of bismuth and 
lead on gold are very similar to each. 
other, and deserve to be noticed.’ Both 
these metals diminish the specific gravity 
of standard gold inversely as the quan- 
tity employed, till the proportion of half 
a grain of lead or bismuth in the ounce. 
Thus an ounce of alloy, 18dwt. 10grs. 
“fine, with four grains of lead, is of the 
specific gravity 17.032; and when the 
lead is diminished to halfa grain, the spe- 
cific gravity is 16.627, being the mi. i- 
mum of specific gravity; for when the 
lead is further diminished to one-fourth 
of a grain, the specific gravity is equal to 
17.039, and a similar.ratio is observed 
with regard to bismuth. 
Having shown that numerous irregu- 
